Method of and materials for treating surfaces of iron, zinc, and alloys of each



Patented Aug. 16, 1949 METHOD OF AND MATERIALS FOR TREAT- ING SURFACESOF IRON, ZINC, AND

LOYS OF EACH Eugene Snyder, Philadelphia, Pa, assignor to AmericanChemical Paint Company, Ambler, Pa., a corporation of Delaware NoDrawing. Application February Serial N0. 648,210

' Claims. (Cl. 148--6.15)

1 This invention relates to a method of as well as to improved materialsfor treating surfaces of metals from the class of iron, zinc and alloysof each, and it involves both a cleaning and a coat- 8 of the surface.More specifically, it is directed to the production of close grainedphosphate coatings on the metal which will inhibit corrosion and act asa bonding film for organic finishing coats of paint, varnish, lacquer,Japan, or the like.

Among the objects of the invention are:

The production of coatings of the type described by the use of solutionsa. which are inexpensive to prepare, and easy to control and replenish.

b. which areso slightly corrosive that they may be handled in ordinarymild steel equipment.

0. which do not form objectionable quantities of insoluble "sludge" innor incrustations on the equipment used. Thus, no difficulties arise dueto clogging of screens and spray nozzles, or to hard scale on heatingcoils, or to abrasion of pumps.

A further object of the invention is to make possible the production ofuniform, very finely crystalline coatings on surfaces which may not becompletely free of grease, oil, dirt and the like. By contrast, priorphosphate coating processes have required rigorously clean surfaces ifthe coating is to be satisfactory at all. Moreover, in order to assureeven, fine-grained coatings, where strongly alkaline or acidic cleaningagents have been employed prior to the coating step per se, it has beennecessary to provide a subsequent rinse at a carefully controlled pH oreven that a special chemical treatment be given to the work followed bysuitable rinses. The need for such special techniques is entirelyeliminated by the improvements of the present invention, whichimprovements make possible a simultaneous cleaning and coatingprocedure.

Still another object is to provide a method of and materials fortreating ferrous and zinciferous metal surfaces by the use of which thetendency for the coated work to develop a discolored blush" while stillwet or to rust while in storage before final finishing is greatlyminimized. At the same time my new process and compositions have theability to improve the life and enhance the quality of applied organicfinishes.

The invention is based very largely on the discovery that a solutioncontaining both primary and secondary phosphates from the class of thealkali and ammonium phosphates will produce on ferrous and zinciferousmetal surfaces an excellent close-grained, water insoluble adherent 2 7coating. Further investigation has disclosed that when the solution ismaintained within the pH range 5 to 6, and is higher than thatcorresponding to the mono-basic phosphates present alone and lower thanthat corresponding to the dibasic phosphates alone, the coatingsproduced are of exceptionally good quality. A further advantage of theuse of such solutions within this pH range is based upon the discoverythat a concentrated material suitable for making up the original bath isalso ideally suited for replenishing constituents removed by reactionwith the metal, by dragout, etc. A solution replenished in this mannerremains within the specified pH range. This is particularly importantwhere a long succession of surfaces must be processed in the samesolution since make-up and replenishment may easily be carried out byunskilled labor by adding the same concentrated material.

It has been found that solutions of primary and secondary alkali orammonium phosphates hav ing 8. DH as indicated above have the ability toremove grease, oil and dirt from the surfaces being treated whilesimultaneously coating them, provided the degree of contamination fromsuch substances is not too great. However, I have discovered that thesolutions which I employ lend themselves exceptionally well to asimultaneous cleaning and coating operation if there be added to them awater-soluble wetting and emulsifying agent, whereupon they willsatisfactorily simultaneously clean and coat even very highly or grosslycontaminated surfaces. Insofar as I am aware, the simultaneous cleaningand coating herein disclosed has never before been successfully attainedand constitutes a major forward step in this art.

I have further discovered that when a solid, nearly insoluble, normalphosphate from the class of iron and aluminum phosphates is present in asolution of alkali and/ or ammonium phosphates such as is describedabove, the pH is not appreciably changed and the coatings produced onferrous and zinciferous metal surfaces are further impoved as regardscorrosion resistance and the life of applied organic finishes. Anytendency for the coated surfaces to "b1ush or discolor while they arewet is likewise minimized.

The coating action of my improved cleaning and coating solutions may beaccelerated by the presence therein of small quantities of oxidizingagents such as soluble nitrites, nitrates, and organic nitro compounds.As preferred agents of this class sodium nitrite, sodium nitrate, andpicric acid are recommended. Recommended quantitles of such agents arefrom 0.01 to 0.25% of sodium nitrite or the equivalent of other solublenitrite; from 0.1 to 1.0% of nitrate calculated as sodium nitrate; from0.1 to 0.5% of picric acid. (These quantities represent concentrationsof these accelerators in the dilute treating bath.)

Acceleration of coating may also be effected by the presence in myimproved coating solutions of small quantities of certain metallic ions.The dissolved metals which have been found useful in this connection arecopper. silver, nickel, and ferrous iron. These metals are only solublein the phosphate solutions of pH to 6 in very small amounts. The amountof dissolved accelerating metal to be used should be from 0.0002 to0.01% of the solution. The use of silver or copper as acceleratingagents may reduce the corrosion resistance of the coating produced. Bothtypes of accelerating material may be used simultaneously.

For convenience in storage and transportation concentrated admixtures.either solid or liquid, may be prepared for making up and replenishingsolutions used in my improved coating process. Examples of suchadmixtures are given in subsequent formulas.

All of these formulas are designed with the following points in mind.While my improved coating process is relatively insensitive to thepresence of dissolved or suspended impurities, yet the continualreplenishment of the operating solutions with the make-up and/or thereplenishing material containing large amounts of inert diluents.soluble or insoluble, leads to an undesirable accumulation of such inertmaterial in the solution. Therefore, experience has shown that materialsto be used for make-up and replenishment of the working solutions usedin my improved process should contain at least 75% of the total. primaryand secondary phosphates from the class: of alkali and ammoniumphosphates.

An example of a solid admixture suitable for preparing coating solutionsin accordance with my invention is given in the following formula:

A solution of the above material in water is prepared. The strength ofthe solution may vary widely depending on the conditions of use.

If the metal is to be coated in a bath by immersion, I prefer to usefrom 2 to 8 ounces of the material of Formula No. 1 per gallon of water.When using spray equipment in which the solution is impinged against thework, I prefer a solution of from 0.5 to 2 ounces of the concentratedadmixture per gallon of water. The solution may be used at roomtemperature although its action is accelerated by heat and I prefer touse it at a temperature of from 120 to 200 F., although thesetemperatures are not to be considered as limitlng.

It is to be understood, of course, that before attempting to employ myinvention the surfaces to :be treated should be freed of rust and scalein any manner familiar to the art, as by pickling, sand blasting orother conventional means. This will be assumed in connection with all ofthe formulas given in the present specification.

When employing a solution prepared from the concentrate of FormulaNo. 1. I find that the work should be relatively free of oil, grease anddirt, that is, it should not be grossly contaminated. However, workwhich is only slightly soiled may be quite satisfactorily treated withsolutions prepared from Formula No. 1, especially if the solution isviolently impinged upon the surface or, in the case of an immersion, ifthe bath is rather violently agitated. Rigorous pre-cleaning, however,is not required as has been necessary in the technique heretoforefamiliar in the art.

In using the impingement method any suitable spraying equipment may beprovided, the details of which are not illustrated because they may takevarious forms dependent upon individual requirements.

Circulation of the solution through the tanks to the spraying orificesis preferably provided by means of a centrifugal pump. and the materialwhich runs down from the work is collected in suitable troughs andreturned to the tank or reservoir from which the solution is pumped.

The work to be treated is subjected to the impinging action of the jetsof solution for a period of from 30 seconds to 1 minute, although thistime may vary considerably depending upon conditions, temperature or thesolution, and the type of material being treated.

While materials such as stampings are being cleaned and coated, thepumping system is kept in continuous operation in order to provide forcontinuous circulation of the solution from the tank to the impingingnozzles at a steady and uniform rate thus allowing the coating operationto take place in a remarkably short period of time. The formation oflittle or no sludge or incrustation, due to my improved process, allowsalmost continuous operation.

After the coating operation is begun, whether .by dipping or spraying,the solution when it becomes weak, as shown by periodic chemicalanalysis, may be kept up to strength by the addition of the appropriatequantities of the concentrated material.

Examination of Formula No. 1 and subsequent formulas will show that themolar ratio of primary and secondary phosphates lies between 32:1 and5.6:1 inclusive. The pH of the coating solution made from Formula No. 1and subsequent formulas will lie between 5.0 and 6.0 inclusive andshould be kept within these limits in order to secure optimumperformance of the cleaning and coating operation. Furthermore, the pHshould be greater than that corresponding to the monobasic phosphatepresent alone and lower than that corresponding to the di-basicphosphate present alone.

The organic detergent of the above formula may be of the class of thewell-known organic detergents of good wetting and emulsifying ower. Asexamples of wetting agents suitable for use 11 the above formula, we mayemploy sodium alkyl sulfates such as sodium lauryl sulfate; sulfonatedhydrocarbons such as alkylated naphthalene sulfonic acids, etc..'andnon-ionic" detergents which are derivatives of poly ethylene glycol.Certain cation-active materials are likewise suitable. In general, anorganic detergent suificiently soluble and stable at the p of thesolution and of adequate surface tension depressant and emulsifyingpower may be used.

The active ingredients in thisand subsequent formulas are put into thesolvent in the same ratio that was shown under Formula No. 1.

Solutions made from this formula and similar ones will act in practicein a similar manner to that given under Formula No. 1 but will have theadded advantage of cleaning even heavily contaminated metal surfacessimultaneously with the coating action. This will eliminate thenecessity for a critical pre-cleaning. In actual practice, if the metalsurface is grossly contaminated with oil, grease, dirt. or other similarmaterial, I have found it expedient to give the material a crudepro-cleaning which usually may be accomplished by spraying the surfacewith hot water and allowing the water to drain oil. This will avoid theaccumulation of large quantities of the contaminants in the workingsolution.

Another benefit obtained by the use of this formula is that theinclusion of hepta decanol or other like substances will cut down on thefoaming tendencies of the solution. Other anti-foaming agents useful inthis invention are petroleum fractions, pine oil, and alcohols of from 8to 18 carbon atoms.

Formula No. 3

Lbs. Primary ammonia phosphate 0.835 Secondary sodium phosphate 0.045Normal aluminum phosphate 0.010 Sulfonated castor oil-- 0.080 Oleylalcohol 0.010 Pine 0.020

Total 1.000 3 In using this formula in my improved process the dilutionof active ingredients and use of the diluted solution are accomplishedin a manner similar to the instructions given under Formula No. 1.However, by the use of this formula a more corrosion-resistant bondingfilm is obtained. Increased resistance to "blushing and after-rusting ofthe coated metal prior to painting, etc. is also obtained.

To Formula No. 4 add 0.80% by weight of copper sulfate pentahydrate.

Formula No. 4 is used and acts similarly but coats more rapidly thanFormula No. 3. This formula is included as an example wherein sodiumnitrite is used as an accelerator and where is wished to obtain a heavyphosphatic bonding coat.

Formula No. 5 acts similarly to Formula No. 4 except that theapplication of the bonding coat is accomplished even faster than whenFormula No. 4 is used. However, I have found that the coating obtainedfrom using Formula No. 5 is less corrosion-resistant than thatobtainedbyusingaformulasimilartoflai.

The corrosion resistance of metal surfaces treated with any of thepreceding formulas in accordance with the instructions given may bestill further improved if given an after treatment with weak chromicacid as taught in tin co-pending application of Messrs. Douty and Romig,Serial No. 583,458, filed November 14, 1944, subsequently issued asPatent No, 2,403,426.

My improved process and materials are capable of producing afine-grained, corrosion-inhibiting coating while simultaneously cleaninga contaminated ferrous or zinciferous surface without the necessity ofpaying particular attention to a critical pre-cleaning step. Thispresents a distinct advantage over any prior technique with which I amfamiliar. The advantages of the invention make it possible either toeliminate entirely a pre-cleaning step or to combine a precleaning stepwith the coating step in one simple unit. This, of course, effects acorresponding saving in floor space and a marked economy in constructionand equipment costs.

What I claim is:

1. The method of providing metal surfaces from the class of iron, zinc'and alloys of each with a corrosion resistant and paint bonding fllmcomprising treating the surfaces with a dilute aqueous solutionconsisting essentially of primary and secondary phosphates from theclass which consists of alkali and ammonium phosphates and containingadded solid, undissolved, normal phosphate from the class consisting offerric phosphate and aluminum phosphate, the pH of the 5 said solutionbeing between 5.0 and 6.0 and being greater than that corresponding tothe monobasic phosphate present alone and lower than that correspondingto the di-basic phosphate present alone.

2. The method of simultaneously cleaning metal surfaces from the classof iron. zinc and alloys of each and providing them with acorrosion-resistant and paint bonding film comprising treating thesurface with an aqueous preparation containing as its essential activeingredients both primary and secondary phosphates from the class whichconsists of alkali and ammonium phosphates, a water-soluble,surface-active emulsifying agent and added solid. undissolved, normalphosphate from the class consisting of ferric and aluminum phosphates,the pH of the preparation being between 5.0 and 6.0 and being greaterthan that corresponding to the monobasic phosphate present alone andlower than that corresponding to the di-basic phosphate present alone.

3. The method of claim 2 in which the said surface-active emulsifyingagent is a watersoluble non-ionic emulsifying agent.

4. A material for making up and replenishing a metal treating solutionbeing an admixture consistingessentially of at least of primary andsecondary phosphates from the class consisting of alkali and ammoniumphosphates, the molar ratio of primary to secondary phosphate beingbetween 32:1 and 5.6:1, the remainder of the composition being composedsubstantially of inert diluent, nearly insoluble phosphate from theclass of normal ferric and aluminum phosphate, emulsifying agent, andanti-foaming material.

5. A material for making up and replenishing a metal treating solutionbeing an admixture consisting of at least 75% of primary and secondaryphosphates of the class consisting of alkali and ammonium phosphates,the molar ratio of EUGENE SNYDER.

REFERENCES CITED The following references are oi. record in the iile ofthis patent:

Number UNITED STATE PA'IIN'I'B Home Dete Allen Jln. I, 1919 Grnvell July13, 1928 Tanner et a1 Nov. 15, 1932 Romig Oct. 11. 193B Neilson Jen. I.1941 Tanner et a1 Nov. 1'1, 1942 Boyle et a1 Dec. 8, 1942 Rnmig Apr. 20,1943 Douty et a1 July 2, 1946

